Panel board



uxamlm Wm UTOSS HGTGTGHCB COATING 0R PLASTIC C. BATCHELLER Nov. 23,1943.

PANEL BOARD Filed Jan. 26, 1939 n w w 77m? 1)? Mia/fa:

//v i/e/v 7-0;? C/emen/ //7e//er ATTORNEY Patented Nov. 23, 1943 i IPANEL BOARD Clements liatcheller, Glens Falls, N. Y., assignor toAllegheny Ludlum Steel Corporation, Pittsburgh,

My invention relates to panel boards or sheets and particularly to animproved panel board of terial adhesively secured to both sides thereof.

0n the other hand, it has heretofore been impossible to produce asatisfactory thin panel board or sheethaving a facing of thin sheetmetal adhesively secured to one side only thereof. Where the backing isa comparatively thick, rigid block or board, a metal facing may beadhesively secured to one side only without distortion or warping. Butwhere the backing board has a large surface area and is comparativelythin so that in such sizes it is flexible or semiflexible, it isimpossible adhesively to apply to one side only thereof a thin metalsheet without causing the composite product to curl or warp due to thestress applied to the unit when the adhesive sets or hardens. Wheremetal sheets are applied to both sides of the board, the warpingstresses developed by the setting of the adhesive are substantiallybalanced and the product is usually free from distortion.

Attempts have been made to apply a metal facing to one side of a plywoodveneer by compositing in a hot plate press by means of such adhesives ashard setting casein glues, soya bean glues, blood glues and eventhermoplastic films of the synthetic resin type. All these cementscontract substantially and become hard in setting, and the productsinvariably have a concave face. Moreover, the wood backing itself is notstable under varying atmospheric conditions and the products, whileconcave in general, become warped and distorted in other directions.

Common cement asbestos boards are not only very dense and brittle butshrink progressively over a long period in the presence of moisture.Moreover, their high caustic content will gradually decompose anyordinary adhesive and thus destroy the bond between the facing andbackmg.

. One of the objects of my invention is to provide a relatively thincomposite panel board of the semi-flexible type having a thin metalfacing on one side only and which will be substantially free fromcurling and warping. Another object is to provide a panel board of thecharacter described Portland cement a., a corporation of PennsylvaniaApplication January 26, 1939, Serial 6 Claims. (01. 154-45.!

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which, in substantial lengths, may be bent or flexed to a smooth curvewithout injury to the backing or to the bond between the facing andbacking. Another object is to provide a panel of the character describedwhich will be capable of withstanding a comparatively high degree ofheat so that it may be applied to wall construction behind gas stoves,hot plates, ovens and the like. A further object is to provide a wallpanel in which the foregoing characteristics will be substantiallypermanent.

I accomplish these objects by means of the novel combination of featuresdescribed below and illustrated in the accompanying drawing in which-Fig. 1 is a fragmentary perspective view, partially in section, showingmy improved type of panel board; and

Fig. 2 is a diagram showing the effect of heat applied to the facing ofmy board.

Referring to the drawing, my board comprises a facing I of comparativelythin sheet metal, say from 0.006 to 0.022" in thickness and prefer-Ingredients Asbestos fibers Bentonite Calcined magnesitc.

Water l Sufficient to plasticize.

The boards are rolled or molded from this composition to a thicknesssomewhat greater than that desired in the finished product and are thenbacking is made of a thickness of from to A" but thicker backings may beused where a less flexible panel is desired.

It will be noted that the asbestos fibers in the backing comprisesubstantially more than 50% by weight of the product and, in thisrespect, my backing differs very substantially from the ordinary cementasbestos boards in which the principal ingredient is Portland cement andin which the fiber content is generally only about 25%, by weight. Thislarge fiber content combined with the bentonite forms a dense appearingbut, in fact, comparativel porous product which, in and of itself, isquite stable against warping or distortion due to variations intemperature, moisture and other factors. The porosity is due largely tothe presence of the bentonitic clay which has the rather remarkableproperty of expanding, when wet, to thirteen or fourteen times itsoriginal volume and shrinking when dried. The high fiber contentcombined with the bentonite also makes a board which can be readily cut,sawed or otherwise worked with ordinary carpenters tools.

After the backing board has hardened, the normal moisture contentthereof is reduced as much as possible by air drying at a temperature ofabout 90 F. The dried boards are then impregnated, by spraying ordipping, with a moistureproofing oil which is capable of being oxidizedwhen heated to a comparatively low temperature, say of the order of 200F. For this purpose, I prefer to use raw linseed oil because of itsavailability and low cost but other oils having similar oxidizingproperties, such for example as tung oil and the like, may be used. Dueto the high porosity of the board backing, the oil will be absorbedthereby after about three minutes immersion. After being impregnated,the boards are dried and the oil oxidized by heating at a temperature ofabout 200 F.

The adhesive employed in securing the facing and backing together is ofthe utmost importance. Any ordinary glues or cements which become hardon setting either at once or after a considerable period of time, areentirely unsatisfactory. Where a panel is of such size and thickness asto be substantially rigid, the character of the adhesive employed is notof such great importance. But where the panel is only to thick and isfabricated in lengths of from 4 to 8 feet, the adhesive employed must beof a permanently plastic or elastic character, otherwise slight flexuresof the panel will cause the adresive to let-go. This is so because, inmy panel, the layer of adhesive is in a plane substantially spaced fromthe neutral axis of the pan l when considered as a beam, and it istherefore subjected to substantial tensile or compressive stresses whenthe panel is flexed.

Hence, it is necessary to employ an adhesive of a permanently plastic orelastic character. Rubber cements which are composed chiefly of latex,as well as asphalts and bituminous materials in general may remainplastic for a while but soon become oxidized or otherwise chemicallychanged so that their resistance to deformation is greatly reduced andtheir bonding properties are also destroyed.

I find that a composition which is composed largely of reclaimed orspent rubber in a petroleum solvent, or preferably, partly of reclaimedrubber and partly of a gum resin in a solvent such as gasoline, carbontetrachloride, acetone or the like and either with or without a smallquantity of lime, forms a pressure sensiapplied both to the facing andto the backing.

After the application of the adhesive, the elements are placed togetheras quickly as possible, to prevent an excessive evaporation of thesolvent, and subjected to a pressure of the order of about one pound persquare inch of surface. The excess solvent in the adhesive to someextent cuts the oxidized vegetable oil in the backing board and isabsorbed or dissipated in this way.

A comparatively light pressure must be used in fabricating my panel dueto the relatively thin gauge metal used in the facing. Where, forexample, stainless steel polished to a mirrorlike finish is used for thefacing, any very heavy pressure ruins the product because the thin metalis pressed into the high and low zones of the backing element. Thesehigh and low zones in the surface of the backing board may not beapparent to the eye, but if the mirrorlike metal, when applied is notperfectly plane, images reflected thereby are distorted and extremelyminute irregularities are immediately discernible.

All pressure sensitive adhesives of the type described have a tendencyto contract somewhat with the loss of solvent therefrom. In thin panelsof my type, this shrinkage or contraction of the adhesive, although veryslight, is, nevertheless, sufficient to effect a slight concaving of thepanel on the metal side. To overcome this condition, I apply to the backof the panel, preferably by spraying, a thin oil-resin film which indrying and contracting will apply to the panel a distorting stresssubstantially equal to but in a reverse direction to the stress appliedby the shrinkage of the adhesive between the facing and backing. Forthis purpose I have found that a film of China-wood oil containing asmall but effective amount of a resin such as dammar or gum copal whenapplied to the back of my panel will produce a product having theinternal stresses therein substantially balanced so that it is a smooth,plane structure.

Although ordinary cement asbestos products such as the ordinary cementshingles are hard and brittle, the cement asbestos backing board in thelarge sizes used in my panels is quite flexible. For example, one of mypanels which is A" thick and 2 feet wide and 8 feet long may be bent orflexed lengthwise into a complete semicyclinder without rupturing thebond between the facing and backing or cracking the backing. In suchcase it will be obvious, if the metal is on the convex side of thecurve, that the adhesive between the facing and backing is subjected tovery appreciable tension and it becomes possible to flex my panels tothis extent only because of the combined properties of the backing boardemployed and the permanently plastic adhesive.

What I claim is:

1. A semiflexible wall panel sheet comprising a facing of thin,corrosion-resisting sheet metal, and a hard backing board formed offibrous material and hydraulic cement; said facing and backing beingsubstantially coextensive and secured together by an adhesive ofsubstantially a facing of thin gauge,

permanent plasticity comprising reclaimed rubber; said backing beingimpregnated with an oxidized vegetable oil and having a resinous film onthe exposed face thereof; said adhesive and said film being socorrelated as to apply substantially balanced curling stresses to saidsheet.

2. A hard,semiflexible panel sheet comprising a facing of thin gaugecorrosion-resisting sheet metal, and a hard, preformed backing boardformed principally of fibrous material with a minor quantity ofhydraulic cement as a binder: said facing and backing being securedtogether by an adhesive of substantially permanent plasticity comprisingreclaimed rubber; and said sheet, when of a length of about eight feetor more and of a thickness up to about one-quarter inch, beingcharacterized in that it may be flexed into substantiallysemi-cylindrical form without rupture of the plastic bond between thefacing and backing or cracking the backing.

3. A hard, semiflexible panel sheet comprising a facing of thin gauge,corrosion-resisting sheet metal, and a hard, preformed backing boardformed principally of fibrous material with a minor quantity ofhydraulic cement as a binder; said facing and backing being securedtogether by an adhesive comprising reclaimed rubber and a resin gum,whereby a substantially permanent plastic bond between said facing andbacking is attained; and said sheet, when of a length of about eightfeet or more and of a thickness up to about one-quarter inch, beingcharacterized in that it may be flexed into substantiallysemicylindrical form without rupture of the plastic bond between thefacing and backing or cracking the backing.

4. A hard, but semi-flexible panel comprising flexible, stainless steel,a hard, preformed backing substantially coextensive therewith containingmore than 50% by weight of fibrous material, a binder of hydrauliccement and a minor quantity of bentonite, and an adhesive ofsubstantially permanent plasticity comprising reclaimed rubber securingsaid facing and backing together; said panel sheet in lengths of eightfeet or more and thicknesses up to about one-quarter inch beingcharacterized in that it may be flexed into substantiallysemi-cylindrical form without rupture of the plastic bond between thefacing and backing or cracking the backing.

5. A hard but semi-flexible panel sheet comprising a facing of thingauge stainless steel, a hard preformed backing substantiallycoextensive therewith and comprising, by weight, more than of fibrousmaterial with a binder of hydraulic cement, and bentonite, and anadhesive of substantially permanent plasticity comprising reclaimedrubber securing said facing and backing together; said backing having onits exposed face a film of resinous material so correlated with saidadhesive as to apply substantially balanced curling stresses to saidpanel; and said panel sheet in lengths of about eight feet or more andthicknesses up to about one-quarter inch, being characterized in that itmay be flexed into substantially semi-cylindrical form without ruptureof the plastic bond between the facing and backing or cracking thebacking.

6. A hard but semi-flexible panel sheet comprising a facing of thingauge stainless steel. a hard preformed backing substantiallycoextensive therewith and comprising, by weight, more than 50% offibrous material with a binder of hydraulic cement, and bentonite, andimpregnated with an oxidized vegetable oil, and an adhesive ofsubstantially permanent plasticity comprising reclaimed rubber securingsaid facing and backing together; said backing having on its exposedface a film of resinous material so correlated with said adhesive as toapp y substantially balanced curling stresses to said panel; and saidpanel sheet in lengths of about eight feet or more and thicknesses up toabout one-quarter inch, being characterized in that it may be flexedinto substantially semi-cylindrical form without rupture of the plasticbond between the facing and backing or cracking the backing.

CLEMENTS BATCHELLER.

